1. Field of the Invention
This invention relates to an indicating instrument assembly of any type and more directly to an assembly structure that decreases the depth required for the instrument assembly.
2. Description of the Related Art
Indicating instruments are used for numerous applications across a variety of industries and within innumerable types of machines, systems, and vehicles. Indicating instruments can, for example, measure the speed of a vehicle, such as an automobile or airplane, or measure the rotational speed of an engine shaft or turbine to indicate a need to switch to an appropriate gear ratio so that the motor is not overworked. Indicating instruments can also be fuel, pressure, and temperature gauges, which are found, for example, on vehicles, heavy equipment, assembly line apparatuses, and other industrial equipment. Complex vehicles and other equipment may have a variety of other special purpose indicating instruments to measure any recordable or gaugable activity or condition. For example, airplanes and submarines may have altitude and depth gauges, respectively.
In many situations it is desirable to construct an indicating instrument as small as possible because of size constraints of the environment in which it is used. For example, in an airplane cockpit a large number of instruments must be placed in an extremely limited area. The size of the indicating instrument is considered not only as a factor of its exposed surface area as viewed by an operator, but also in terms of the amount of space taken, for example, under a mounting surface or behind a panel, by the instrument""s functional and mounting components.
In other instances, it is desirable that the exposed portion of the indicating instrument be quite large so that the operator can easily perceive the presentation of the gauged information. In these situations, although it may be desirable to provide a large display for the information, it may be equally desirable that the indicating instrument be otherwise small in size due to similar constraints of space for housing or mounting the underlying functional components. An example of these competing needs may be seen in the dashboard instruments of an automobile such as speedometers and tachometers where the dial size is desired to be large for easy reading, but the mounting and housing space within the dashboard is limited.
Indicating instruments may also be manufactured for sale on the xe2x80x9caftermarket,xe2x80x9d wherein additional instruments or devices, which were unavailable as options on the vehicle or other equipment at the time of original purchase, are provided for installation by the operator. In the case of aftermarket indicating instruments such as speedometers or tachometers, these gauges may be provided for mounting on top of the dashboard or at another location in the vehicle for ease of viewing by the operator. For example, many aftermarket tachometers are sold to automobile operators involved in stock car racing. In such racing it is important for the operator to know when to shift, but it is imperative that the operator be able to concentrate on the raceway and the competitor vehicles in order to avoid a collision. Many of these racing operators prefer to mount an aftermarket tachometer on top of the dashboard, or otherwise in the area of the windshield, so they do not have to lower their eyes from the road to read an original equipment tachometer mounted within the dashboard.
Prior art indicating instruments 200, such as those shown in FIGS. 1A, 1B, 2A, and 2B, depict aftermarket tachometers with their own housings for dashboard mounting applications. Because of standard design configurations, these indicating instruments 200 are relatively deep in body thickness from the face of the instrument to the back of the housing. The thickness of these instruments 200 is dictated in large part by the size of the meter movement 210, the rear end of which is generally mounted to a printed circuit board (PCB) 230. The meter movement 210 and PCB 230 assembly is then mounted to and within the housing 240 of the indicating instrument 200, generally by mounting screws 220a and 220b, to provide a firm support for the meter movement 210, PCB 230, and related display components of the indicating instrument.
The indicating instrument of FIG. 2B is configured with dual PCBs 230 and 230xe2x80x2, which further increases the necessary depth of the housing to enclose the additional PCB components. Generally a gap is also needed between the PCB 230xe2x80x2 and the rear of the housing 240 in order to allow room for the circuit components mounted on and extending from the PCB 230xe2x80x2, again deepening the housing. The design of mounting screws 220a and 220b, which extend beyond the housing in FIG. 2B, further increase the overall depth of the indicating instrument.
In aftermarket applications, such significant depth of an indicating instrument can make it difficult to fit and install on the dashboard of a vehicle, especially in the case of a narrow dashboard or a steep windshield slope. In applications where the indicating instrument is integrated into the original design of the vehicle, machine, or other system control, the prior art designs of indicating instruments require relatively deep spaces to house their functional components.
The present invention concerns the structure of and methods of constructing indicating instruments with slim profiles. What is meant by xe2x80x9cslim profilexe2x80x9d is that indicating instruments according to this invention are of shallow depth or are relatively thin between the face of the indicating instrument and the rear most component or the back panel of any housing enclosing the indicating instrument.
At a base level, an indicating instrument according to this invention may comprise a meter movement and a circuit board. In order to achieve the slim profile, the main body of the meter movement is situated in an aperture in the circuit board. With this placement, the front end of the body of the meter movement extends a distance in front of the circuit board and the back end of the meter movement body extends a distance behind the circuit board. Through appropriate selection and arrangement of any components on the circuit board, the circuit board can be constructed such that none of its components extend beyond the distance that the meter movement extends on either side of the circuit board. In this manner the space needed for the meter movement and the circuit board and its components collapses into the same area.
In a further embodiment, a light plate may be added to the circuit board and meter movement. The light plate may be seen as a structural framework for the indicating instrument. The light plate is a rigid, refractive material, and in one embodiment is a molded plastic plate with boss mounts and boss extensions molded as protrusions from the back side of the light plate. The circuit board is mounted to the boss mounts extending from the light plate. In this way, the boss mounts provide appropriate spacing between the light plate and the circuit board to allow room for the front end of the main body of the meter movement and any components of the circuit board to reside. The meter movement may also be mounted to the back side of the light plate to provide secure positioning of the meter movement relative to the rest of the components of the indicating instrument. In this manner, the internal components of the indicating instrument are all held together and can be calibrated and tested without the addition of any further components. This provides a benefit in that significant disassembly is avoided in the event that a functional component is bad and needs to be replaced.
In an alternative embodiment, the indicating instrument may have a second circuit board. This second circuit board may be positioned between the light plate and the first circuit board and similarly mounted to boss mounts extending from the light plate. In one embodiment, the terminals of the meter movement may be directly electrically and mechanically attached to the second circuit board.
Aside from its structural function in this invention, the purpose of the light plate is to transmit light from a light source to the face of an indicating instrument to illuminate the dial. In an embodiment of the present invention the light plate collects light from a light source, for example, a light bulb mounted on the circuit board, via a projection from the back side of the light plate that contains an aperture. The aperture is large enough to surround the light bulb projecting from the circuit board. In this manner, the light bulb need take up no more space than the gap provided between the light plate and the circuit board by the boss mounts and taken up by the meter movement and other circuit board components. The edges of the aperture in the light plate surrounding the light bulb collect the emitted light and transmit it through the light plate to its edge around the dial on the face of the indicating instrument where the light is emitted from the light plate.
The indicating instrument may further have a pointer that travels over the dial face. The pointer may be attached to a shaft extending from the meter movement through apertures in the light plate and dial face. The pointer may move in a plane above and parallel to the dial face and underneath a lens. The pointer may be halted in its travel by a pointer stop protruding from the dial face. In one embodiment, the pointer stop is a light emitting diode (LED) that further functions as an indicator of a condition of the indicating instrument. The LED is electrically and mechanically connected to the circuit board and protrudes through apertures in the light plate and dial face. The pointer stop extends above the dial face far enough to intersect the sweep of the pointer and stop the movement of the pointer.
The various components of the indicating instrument may be contained in a housing for protection or for individually mounting the indicating instrument, for example, external to an instrument panel integrated into the machinery for which the indicating instrument is providing measurements. The housing may cover the back of the indicating instrument components and be fitted with a lens through which the face of the indicating instrument may be viewed. In one embodiment, the lens is attached to the housing by a bezel surrounding circumferential edges of the lens and housing, clamping the two together. A gasket may be placed between the lens and both the housing and the edge of the light plate as a cushion and a seal. Also, in one embodiment, the housing may be formed with a circumferential ledge normal to the side wall. The boss extension of the light plate may extend beyond the edges of the circuit board to make contact with the ledge. Due to the clamping pressure of the bezel transferred through the lens and the gasket to the light plat, the light plate, supported by the boss extension, is held firmly against the housing ledge.
In another embodiment of the invention, the lens of the indicating instrument is constructed with a concentric projection around the edge of the face. This projection supports the bezel and prevents the edge of the bezel from scratching or otherwise damaging, for example, gouging or cracking, the optical surface of the lens. In yet another embodiment of the indicating instrument, the concentric projection of the lens may further be a channel bounded by two walls. Either the first wall or the second wall may provide the support to the bezel. In addition, the lens may have a concentric projection around the edge of the lens opposite the channel. With this lens construction, it is possible to place a lens on a relatively flat surface without scratching the optical surface of the lens. It is further possible to stack lenses on top of each other, for example, during shipping of lenses as individual components, with the projection of the second side fitting into the channel of the first side. In this way, the optical surfaces of the lenses are separated from each other and the lenses are unable to rub against each other, thereby preventing scratching and other damage.
An indicating instrument with a housing may be mounted on various surfaces and in various configurations through the use of a mounting strap that surrounds the housing. The mounting strap can be tightened or loosened around the housing through the use of a tightening means. The indicating instrument may be rotated within the mounting strap and secured at any position by tightening the tightening means. In one embodiment, the tightening means may be a bolt with a nut that connects two ends of the mounting strap and draws them toward each other, thereby tightening the mounting strap around the housing. Also attached to the mounting strap may be a mounting foot, which can be attached to various surfaces at various angles. In one embodiment the mounting foot can be secured into a particular position by tightening the tightening means. In the particular embodiment wherein the tightening means is a bolt, the mounting foot may similarly be held to the mounting strap by the bolt and secured when the nut is tightened.
The indicating instrument may further have an external indicator to indicate a condition of the indicating instrument. This may be the same condition or a different condition than the condition indicated by the pointer stop indicator in the embodiment previously described. The external indicator may have a mounting foot that can be held between the mounting strap and the housing of the indicating instrument, wherein the mounting foot is attached to the indicating instrument. In another embodiment, the external indicator can be mounted at a location separate from the indicating instrument, but maintain communication with the indicating instrument, for example, by wires.